These Strainers have been designed to attach to the suction end of the hose when sucking water from a stream,lake,water race etc. The Grill on the strainer is designed to stop small particles from entering and blocking the pump system. The volume of the grill area is designed to ensure there is no restriction to the water flow.
Sizes 32mm 11/4″ 38mm 11/2″ 50mm 2″
http://www.trudesignplastics.com/marine/products/59-strainers